In wiring substrates having a metal wiring pattern formed thereon, the metal wiring pattern is typically coated with a resin coating or insulating film except a portion (contact portion) through which connection with an external element is provided. Whereas the wiring pattern is protected by the coating, the contact portion is exposed and therefore is susceptible to oxidization, corrosion due to exposure to humidity, and further to metal element migration, for example. As a result, problems such as a connection (contact) failure or shorting of adjacent wiring lines can occur.
To solve these problems, approaches to forming a protective film on the contact portion as well have been proposed in the past. For example, Patent literature 1 describes a protective resin film formed to a thickness that can be pierced through by a terminal of a mating connector to be connected. Patent literature 2 describes a fluorine resin thin film of such hardness that it can be cut away by a terminal of a mating connector to be connected.
As has been described, configurations have been used in which a protective resin film is formed on a contact portion to prevent problems such as migration. However, the protective resin film is ripped open or cut away when electrical connection is made. That is, the protective film in the connection portion is removed to expose the contact portion. The exposed contact portion is inevitably subject to development of corrosion. In addition, if the contact portion is repeatedly attached and detached to an external element, the exposed area widens and accordingly the effect of protection is significantly impaired.
Furthermore, because the protective resin film is ripped open or cut away when electrical connection is made, resin particles generated during the ripping or cutting may cause a contact failure.
Another problem is that an external element having a low contact pressure cannot be electrically connected in a reliable manner if the contact pressure is too low to rip open or cut away the protective film sufficiently deep or wide to ensure a reliable electrical connection.
Patent literature 1: Japanese Patent Application Laid-Open No. 2002-109997
Patent literature 2: Japanese Patent Application Laid-Open No. 8-222839